Induction motor control by electric brake



E PELL INDUCTION MOTOR CONTROL BY ELECTRIC BRAKE April 21, 1953 E. PELL.2,636,157

INDUCTION MOTOR CONTROL BY ELECTRIC BRAKE Filed Oct. 16, 1950 3SheejbS-Shee'tl 2 Fraai?,

} IC. cuzcLE mAeQAM i IT =O FIG-i216 ZERo SPEED I? FULL LoAD HOISTING 1^1B 2% Exc. AT

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LOWF.R\N6

. lJNVENTOR. Enzo PeZ,

BY l AT TOPNEY e/o SPEED FULL LOAD o: HOO

oN HooK. "50% SPEED April 2l, 1953 E. PELL 2,636,157 INDUCTIQN MoToBCONTROL BY ELECTRIC BRAKE Filed 0G13. 16, 1950 3 Sheets-Sheet 3 J lF1524' 0*-150 U5 I Uuloo 5u E 1D 5o UU e N 5o mo l5@ MOTOR SPEED FIG' 5--pEcsErqERJNE L1 AMPLIFIER clQcLE IPCl IP? olAGRAM IF A y J/ Is\ 75E miP 1,/ Ir Ig/ l JNVENTOR. ZINC Pea IPCa BY IP |50 lspEED lOOjQ SDEED IPIlma ATTOQNEY Patented Apr. 21, 1953 INDUCTION MOTOR CONTROL BY 'vELECTRIC BRAKE Erie Pell, Shorewood, Wis., assignor to Cntler- N Hammer,lne., liiilwemkee, Wis., a corporation of Delaware Application October16, 1950, Serial No. 190,361

9 Claims.

. his, invention. relates to, means for controlling the speed ofelectric motors and, more specically, to control systems which areprovided With elec'trornagnetcally operating load brake, such as an eddycurrent brake vor clutch, as one @if the Speed controlling devices.

lt has heretofore been proposed to regulate the speed of alternatingcurrent motors of the slip ring induction type by mechanically couplingthereto an electromagnetic load brake, as, for example, a` brake of theeddy current type; and various arrangements for automatically excitingthe coil lor winding of such brake to achieve the desired regulationhave been proposed.

lt, is an object of the present invention to provide novel means forenergization of the coil of braises of the aforementioned character toafiord the desired motor speed regu-lation, and more particularly toafford excitation of such brake coils proportional to the motor speedand without use of pilot generators, speed tachometer generators,frequency relays, or other devices functioning on the frequency orvoltage ofthe .motor secondary.

Another object ofthis invention is to afford brake coil excitation inproportion tomotor speed as aforementioned deriving the controllingcoinponent of such excitation from the rnotor primary in a novelvmanner, thereby to afford brake coil excitation proportional to motorspeed beyond synchronous speed of` the motor and into the regenerativequadrant tocover the entire speed ran-ge of` the motor.

A still further object ofthe invention is the utilization oi a novelmethod of deriving, a current proportional to the speed off thernotorfor energization oi an electromagnetic load brake to aiiord speedregulation o ig'- a motor having appropriate secondary resistance?, andmore par'- ticularly to derive suchy current by balancing a currentderived from the line voltage, against a load. current derived from themotor prima-ry,A which currents cancel one another at vzero speed thusproducing a netoutput controli currentproportional to motori speed-Other objects andv advantages of the invention `will be apparentA fromthel embodiments shown in thev drawings andvdescribedl herein,- after,it being understood that while the embodi'e ment described relatestoaholst control the invention has a broader application and is to beafforded coverage withixrthe scope` off the appendedclaims.

InL the drawing;

(o1. sisfcz) .Figure 1 illustrates diagrammatically a hoistine' controlsystem embodying the invention;

Fig. 2 generally depictsl in graphic form the derivation oi brakeenergizaticn current afforded by the control system illustrated in Fig.l, while Figs. 2R, 21? and 2,c depict such energization derivation atvarious, motor Speeds;

Fig. S; illustrates the operating characteristics afforded by thecontrol system of Fig. l;

Fig. 4 depicts the proportionality of clutch or braise excitation tomotor speed as aorded by the invention;

Fig. 5 diagrammatically illustrates a modiication of the control systemillustra-ted in Fig. i which may be preferred' under certaincircumstances to be hereinafter described; and

Figs. 6, 6a, 6b and. 6? are similar to Fig. 2 and depict the, brakeexcitation derivation of the system illustrated in Fig. 5'.

in the embodiment. of the invention diagrammatically shown in Fig. 1 analternating current induction motor lil preferably of the slip ring typeis employed. Mounted on one end of the motor shaft H is a mechanicalbrake lil of conventional form adapted to` be released by supplying,current to the Winding lie thereof, While mounted on the other end ofshaft li is a torque resisting means` or load brake i3 of suitable orrnand having an exciting winding ida. Also` mounted on sha-it ll is ahoisting drinn lll upon. which a line sustaining load is wound.

The motor luis preferably supplied with electrical energy froin.L1,L2,L3, through one or'the other ci the contactors ory L for operation ofthe. motor lll in reverse directions selectively, the contactors H and Lbeing under thev control of a conventional drum controller enclosedWithin the dotted line rectangle l5, it being apparent thatenergirzationof the contacter EL or contacter L as the case,- may be,Iwill inv the embodiment ci the invention illustrated, affordV hoistingor lowering. respectively,4 of the load on drum l5.

Controleer the speedofAv motor IQ, disregarding for thefniornent thecontroladorded by the torque resisting` brake; on clutchV E3., is.providedin conventional manner by varying the secondary resistance or"the motor,` the resistor grid rangement: referred' to; generally by the.reference numeral-18; together with. relays IA, IB, EC, il" underthecontrol. or the'druin4 controller for successively cutting outresistance in the usual mannerfwithA advance or thedrum controller from:its oii position being employed;

As will also be apparent, movement of 3 controller l in either directionfrom its off position energizes the brake relay BR, to close the circuitto winding 22 of mechanical brake l2 for release thereof.

As aforeindicated, further refinement of control over the speed of motorI0 under varying load conditions is afforded by the torque-resistingmeans i3 which may be of the eddy-current clutch type, powder metalclutch type or any other suitable torque resisting device capable ofbeing energized in different degrees of excitation.

As also aforeindicated, the torque-resisting means i3 has an energizingcoil or winding lS which is preferably afforded excitation by a D. C.current obtained generally from the A. C. source L2, L2, throughsuitable rectiiiers indicated generally by the reference numeral Il. Apotential transformer PTl is preferably utilized for derivation of theaforementioned current as shown, but

a direct connection to the line may be employed if desired.

Combined with the aforementioned current derived from the voltagebetween phases 2 and 3 is a second current component, which isproportional to the load of phase 3 .and is derived through atransformer CT connected in phase 3 of the motor primary as shown inFig. 1. The motor is operated with a secondary resistance of 100%resulting in a stalled motor primary current of 100% rated motor currentas indicated in Fig. 2. Assuming a motor no-load, or exciting current ofabout 41.5% of rated motor current, this primary current Will be inphase with the voltage between L2, L3. By proper adjustment of aresistor R1 (Fig. 1), the current due to the phase voltage (2 3) can bemade equal to that of the current transformer CT secondary with themotor stalled. This condition is illustrated in Fig. 2a. With the motorstalled these two currents will therefore cancel in the rectifier l? andclutch coil |35, leaving a current circulating in the transformer CT andresistor R1 back to the line.

As the motor accelerates to synchronous speed, the primary current ofmotor l0 will follow a locus as shown by the circle diagram (Fig. 2).For any other condition than standstill the combination of the currentderived from the voltage between L2 and L3 and that derived from theload of phase 3 of the motor primary through transformer CT will,therefore, result in a current component flowing through the rectifierIl and the clutch coil E32 which, as shown in Fig. 1, is connected toreceive the output of the rectifier I?. For example, at synchronousspeed the clutch coil current will be proportional to component (IT) ofFig. 2b; at 150% speed, this component will have further increased asshown in Fig. 2. The output current of the rectier will, therefore, varysubstantially linearly with speed; that is, the rectied current of theclutch coil will be proportional to motor speed as shown in Fig. 4.

It should be noted at this juncture that clutch coil I3a may beconnected through resistor R3 directly to rectifier Il to receive theoutput thereof; or an amplifier of suitable form may be interposedtherebetween as shown in Fig. 1 if deemed necessary, as for example,when the clutch coil is such as to require considerable amount of powerfor excitation thereof.

When an amplifier is utilized a resistor R2 may be employed to affordadjustment and improve the response of the amplifier. The amplierutilized may be of any suitable form, as for example, a magneticamplier, in which the operating portion of the characteristic isessentially linear and which may be biased so that its control currentmay be shifted so as to give zero or minimum output with zero input.

Referring again to Fig. 1, it will be seen that current to the clutchcoil 13a is in some cases by-passed through resistors R4, R5, R6, andR'7 in accordance with the operation of relays 2L, 3L, di' and 5L, aswill hereinafter be described.

It will, of course, be understood that the amount of torque developed bythe clutch I3 depends upon its field current as Well as the speed of theclutch armature. The stronger the eld and the greater the speed, thegreater the torque, as illustrated in Fig. 3.

On the rst point lowering, maximum braking torque is required and so theentire output of the rectier is fed into the clutch iield 32, with thecomponents as selected for Fig. 3. This results in excitation of theclutch at approximately 20% speed. Since a stalled torque is providedfor kick-0H, the net braking torque will be less than the developedclutch torque at this speed, as indicated in Fig. 3.

Moving the master or drum controller to the second speed point loweringcloses reiay 2L to bypass some of the current through the clutch coil.This reduces the excitation of the clutch to approximately 100% at 60%speed, and thus the relative braking torque of the clutch, to provide aspeed torque curve as shown by 2L (Fig. 3). Further advancing the masterto the fifth speed point will close relays 3L, LlL and 5L successivelyto lower the iield current of the clutch I3 and produce speed torquecurves as indicated by curves 3L, 4L and 5L (Fig. 3). This method ofusing a parallel circuit to regulate the current of the clutch is, ofcourse, advantageous since the output of the current transformer CT ismore or less independent of the circuit resistance as the currenttransformer tends to build up a higher secondary voltage to maintain agiven ratio between its primary and secondary currents.

If desired to also utilize the eifect of the clutch i3 in the hoistingdirection for extra slow speed on the rst two speed points, relays 2L to4L may be energized as shown in Fig. 1. On the third speed point, thecurrent transformer CT and rectifier H may be short-circuited bycontactor IB which is provided with a set of auxiliary contacts I8 asshown to completelyeliminate the effect of the clutch and permit fullhoisting speed of the motor. The performance afforded by theaforedescribed arrangement is shown in Fig. 3 (hoisting quadrant).

As will be apparent from the foregoing description the clutch I3 acts asan electrical load brake. With an overhauling load, the speed of themotor will stabilize at a value such that the braking torque of theclutch i the developed motor torque is equal to the overhauling torqueof the load on the hook. For example, at zero motor torque, i. e., ahook load equal to the friction torque, the speed will stabilize at avalue for which the motor torque is equal to the braking torque of theclutch I3. This is depicted in Fig. 3. The dotted curves represent thebraking torque of the clutch or load brake i3 plotted against motorspeed for some given constant value of the clutch eld current, while thedotted assent? straight lines represent the speed torque curvesof themotor. The net braking torque show-n by the heavy curves is obtained as.the diierence between the braking torque of the clutch and the drivingtorque of the motor. Since the clutch iield current as obtained by thedisclosed connection of transformers and rectifier is proportional tospeed, these curves are identified with a given field current at somegiven speed ofthe motor. For example, curveA [L is based on a fieldcurrent of.r 100% at 20%y speed. An examination will show that the nettorque of iL at speed is equal to the difference betweentheclutch torqueand the driving torque of the motor at this speed. Assuming, forinstance, a speed of twice this value, the eld current will also doubleand the clutch torque correspondingly increase as indicated bytheflatness of this speed torque curve. At lowering speeds beyond the minus100%, the motor torque reverses and the net braking torque becomes thesum. of the clutchV and motor torques. The speed torque. curves in thehoisting direction will become an image of those the lowering direction,all thingsV being equal.

Referring now to Fig. 5, there is illustrated a modification of thesystem shown in Fig. 1. to afford operation similar to that afforded bythe System of Fig. 1 under other conditions to be hereinafter described,it beingv understood that the showing of Fig. 5 is only fragmentary ascompared with Fig. 1, and that Fig. 5 has'been abbreviated merely torender the same an'expedient illustration of` the modification about tobe described. It will be noted that similar elements of Fig, l and Fig.5 have been giveny the same reference characters.

As previously pointedout, the system of Fig. l, and more particularlythe relations depicted in Figs. 2, 2a, 2b and 2c, are based ona motorexciting current of 41.5%. For motors departing considerably from thisvalue, as for example, motors with lower or lessfavorable ,power factor,

i. e., requiring a large, exciting current as indi.

cated in Fig. 6, it may be desirable to employ additional means forlining up the stalled-motor primary current and the line voltagecurrent. As shown in Fig. 5, such means; may take the form of anauxiliary potential transformer PTZ, the primary winding of which isconnected across L1, L3, and the secondary winding of which is connectedinto the secondary circuit. ofl PT1 as shown.

The auxiliary potential transformer P'I2 will injectl a voltage andcurrent component Ipcz (Fig. 6) into-the network 'to be combined withthe current from PTl to produce a resultant current completely vorpartiallyy (as desired) matching the primary current ofthe motor andresulting in a clutchcoil currentwit'h a stalled motor, as shown in Fig.6a. For 100% and 150% speed the clutch coil current would vary asindicated in Figs. 6b and 6, respectively. Lesser amounts ofcompensation may be obtained, if desired, by Variation of the resistorR8 in series with the potential transformer secondaries, as shown inFig. 5. All other elements of the control system may be as shown in Fig.1, it being necessary here merely to note that the resistors R1 to R7are shown in Fig. 5 as an adjustable resistor R1o for expediency ofillustration. Thus motor performance corresponding to that shown in Fig.3 may be afforded under varying conditions as aforementioned.

It will be apparent from the above-described embodiments andmodii'cation that speed control systems according to the-invention canbe a1- tered and modified with respect to various details, withoutdeparting from the principles -of the invention and within the scope ofits essential features set forth in the appended claims.

I claim: v

1. The combination with an alternating current motor and torqueresisting means mechanically connected with the shaft of said motorincluding windings adapted upon excitation to vary the braking eiect ofsaid torque resisting means, of means affording a, current of selectedproportionality in magnitude and corresponding in direction to thevoltage of a phase of said motor, means affording for combination withsaid current a second current proportional in magnitude andcorresponding in direction tothe load current of one side of said phaseof said motor, and meansV to combine such currents to obtain a resultantcurrent substantially proportional to the speed of said motor and 'tosubject the windings of said torqueresisting means to said resultantcurrent to afford. excitation of said torque resisting means to controlthe speed of said motor throughout its entire speed range.

2. In an electrically driven hoist, the combination with an alternatingcurrent motor and torque resisting means mechanically connected with theshaft of said motor including windings adapted upon excitation to varythe breaking effect of said torque resisting means, of means providing acurrent ofselected proportionality in magnitude and corresponding indirection to the voltage of a phase of saidmotor, means for deriving acurrent from the motor primary proportional in magnitude andcorresponding in direction to the load current of one side of said phaseof said motor, and means for. combining said aforementioned currents anddelivering to said windings of said torque resisting means a rectifiedcurrent substantially proportional to the speed of said motor thereby to`afford excitation of said torque resisting means to control the speedof said motor throughout its entire speed range and under Varying loadconditions.

3. The combination with an alternating current motor and' torqueresisting means mechanically connected with the shaft of said motorincluding windings adapted' upon excitation to vary the braking effectof said torque'resisting means, of means for delivering to the windingsof said torque resisting meansA a rectified current substantiallyproportional to-the speed of said motor, said means including means forobtaining and combining a current proportional in inagnim tude andcorresponding in direction tothe volt age of a phase of said motor and acurrent proportionai in magnitude and corresponding in direction to theload current lof onefsideof said phase of the motor, and furthercomprising means for balancing said two currents so that they canceleach other at zero speed of the motor.

4. The combination with an alternating current motor having speedcontrol means including means for varying the secondary resistance ofthe motor and torque resisting means mechanically connected with theshaft of said motor including windings adapted upon excitation to varythe braking effect of said torque resisting means, of means affordingexcitation of the windings of said torque resisting means with a rectiedcurrent substantially proportional to the motor speed, said lastmentioned means com- Iprising means forf-derivinga current of selected"proportionality in magnitude and corresponding in direction to thevoltage of va phase of the motor, means for deriving a second currentpro- `said resultant current applied to said windings in a predeterminedrelationship to the variation Yin secondary resistance of the motoraorded by said secondary resistance varying means.

5. The method of exciting windings of torque resisting means connectedto a motor for control of the speed thereof which comprises combining acurrent of selected proportionality in magnitude and corresponding indirection to the volt age across a phase of the motor with a currentproportional in magnitude and corresponding in direction to the loadcurrent of one side of said phase of the motor, rectifying the resultantcurrent, and exciting said windings therewith to aord energization ofsaid torque resisting means substantially proportional to the speed ofsaid motor. Y

6. The method of exciting windings or" torque Aresisting means connectedto a motor for controi of the speed thereof which comprises deriving acurrent proportional in magnitude and corresponding in direction to thevoltage across a phase of the motor, deriving a second currentproportional in magnitude and corresponding in direction to the loadcurrent of one side of said phase of the motor speed, balancing thecurrents so derived to cancel each other at zero motor speed to obtain aresultant current substantially proportional to the motor speed,rectifying the resultant current, and subjecting said windings theretofor energization of said torque resisting means.

7. The combination with an alternating current motor having iirst,second and third input leads and torque resisting means mechanicallyconnected with the shaft of said motor inciuding windings adapted uponexcitation to vary the braking eiect of said torque resisting means, ofmeans affording a current proportional in magni tude and correspondingin direction to the voltage between said rst and second input leads ofsaid motor, means connected in said first input lead of said motorprimary for deriving a current proportional in magnitude andcorresponding in direction to the load current o1" said first inputlead, means connected across said first and third input leads and ofsaid motor primary for deriving a compensating current, and means forcombining said three currents to produce a resultant currentsubstantially proportional to CTL ` motor speed for delivery to saidwindings thereby affording energization of said torque resisting meansto control the speed of said motor throughout its entire speed range.

8. In an electrically driven hoist the combination with an alternatingcurrent motor having first, second and third input leads and torqueresisting means mechanically connected with the shaft of said motorincluding windings adapted upon excitation to vary the braking effect ofsaid torque resisting means, of means affording a current proportionalin magnitude and corresponding in direction to the voltage between saidrst and second leads of said motor, means connected in said first inputlead of said motor primary for deriving a current proportional inmagnitude and corresponding in direction to the load current of said rstinput lead, means connected across said rst input lead and the thirdinput lead of said motor primary for deriving a compensating current,means for balancing said rst and third currents against said secondcurrent to cancel one another at Zero motor speed thereby affording aresultant current substantially proportional to motor speed, and meansfor rectifying said resultant current and subjecting said windingsthereto for energization of said torque resisting means to control thespeed of said motor throughout its entire speed range.

9. The method of exciting windings of torque resisting means connectedto a motor having first, second and third input leads for control of thespeed thereof which comprises, deriving a current proportional inmagnitude and corresponding in direction to the voltage across said irstand second input leads of said motor, deriving a second currentproportional in magnitude and corresponding in direction to the loadcurrent of said first input lead, deriving a compensating currentproportional in magnitude and corresponding in direction to the voltageacross said rst and third input leads of said motor, balancing saidfirst current and said compensating current against said second currentto cancel one another at zero motor speed to produce a resultant currentsubstantially proportional to motor speed and rectifying the resultantcurrent for delivery to said windings for energization of said torqueresisting means.

l ERIC PELL.

References Cited in the iile of this patent UNITED STATES PATENTS NumberName Date 2,458,454 Winther Jan. 4, 1949 2,488,210 Leitch Nov. 15, 1949,2,488,238 Rathbun Nov. 15, 1949 y2,493,607v Wendelburg et al. Jan. 3,1950 2,534,423

Douglas et al Dec. 19, 1950

